Timed-bioresorbable microspheres are being investigated as a vehicle for delivery of radioisotopes, particularly, Y-90 for localized radiotherapy. Microspheres of several calcium phosphate glasses prepared in Phase I have been shown to retain 99.0 to 99.9% of yttrium in vitro. They are non-toxic and bioresorbable. These microspheres must maintain similar structural integrity and yttrium release characteristics in vivo before they are clinically useful, since leakage of radioactivity from injection site reduces therapeutic efficacy, induces undesirable damage to normal tissues, and increases the risk of side effects and secondary neoplasia. Characterizing the release of Y-90 in vivo and identifying the relationship between in vitro and in vivo bioresorption rates will provide valuable input for glass composition optimization, and will set the criteria for bioresorption control through nano-scale chemistry. A team of distinguished collaborators gas been formed to lead in the safety and efficacy evaluations of using timed- bioresorbable Y-90 microspheres for treating solid tumors, arthritic joints, etc. Animal experiments are designed to address a variety of safety issues and adequate efficacy studies are also proposed. XL Sci-Tech expects to produce pilot quantities of timed-bioresorbable Y-90 microspheres that are safe for clinical investigations by the conclusion of the Phase II study. PROPOSED COMMERCIAL APPLICATIONS: Timed-bioresorbable Y-90 microspheres will deliver highly localized beta radiation without risk of activity leakage. These microspheres are ideal for direct intratumoral injection in treatment of cancers of liver, pancreas, etc., and radiation synovectomy of rheumatoid arthritis.